ITK nightly version update

This commit updates:
  (1) SHA used in CMakeLists.txt to checkout ITK sources
          (InsightSoftwareConsortium/ITK@bb54bad693)
  (2) VERSION variable set in itkVersion.py

It was automatically generated by the script update_python_version.sh [1]

[1] https://github.com/InsightSoftwareConsortium/ITKPythonPackage/blob/2d93461/scripts/update_python_version.py

Author: kwrobot

CMakeLists.txt

@@ -74,8 +74,8 @@ if(ITKPythonPackage_SUPERBUILD)
 
   set(ITK_REPOSITORY "https://github.com/InsightSoftwareConsortium/ITK.git")
 
-  # ITK nightly-master 2021-04-29
-  set(ITK_GIT_TAG "8fd1fec6b7")
+  # ITK nightly-master 2021-05-03
+  set(ITK_GIT_TAG "bb54bad693")
 
   #-----------------------------------------------------------------------------
   # A separate project is used to download ITK, so that it can reused

itkVersion.py

@@ -1,4 +1,4 @@
-VERSION = '5.2.0.dev20210429+55.g8fd1fec6b7'
+VERSION = '5.2.0.dev20210503+58.gbb54bad693'
 
 def get_versions():
     """Returns versions for the ITK Python package.